Multivariate examination of response surfaces around the reaction conditions for the Scandinavian Society's recommended method for creatine kinase determinations.

We examined the reaction surfaces around five variables (imidazole, ADP, creatine phosphate, magnesium, and pH) in the Scandinavian method for determining creatine kinase, using factorial experimentation (five level, five factor) at reaction temperatures of 30 and 37 degrees C. Theoretical response surfaces were computed by fitting a quadratic polynomial equation to the experimental data by least-squares regression. Essentially no differences were apparent in the theoretical curves among the five specimens we analyzed, or between reaction temperatures. Our response-surface data showed the following: for pH and imidazole, activity optima in the region of the Scandinavian conditions; for creatine phosphate, a broad plateau over the concentration range investigated (10 to 50 mmol/L); and for magnesium and ADP, gently increasing contours with maximal creatine kinase activity at concentrations greater than those investigated in our study (magnesium 15 mmol/L, ADP 3.5 mmol/L).